“We have known for some time that viruses act like a vaccine. If you inject a virus into a tumour, you can provoke the immune system to destroy that cancer and other cancers,” according to Dr. Stephen Russell of the Mayo Clinic.

His patient, 50-year-old Stacy Erholtz had been fighting multiple myeloma – a cancer in her bone marrow – for about a decade. This Mayo Clinic trial she signed up for in June was her last ditch effort.

She and another myeloma patient were selected for the study because they are immune-compromised and can’t fight off the measles before it has time to attack cancer. Erholtz was the only patient to head into remission.

The measles zero in on the cancer tumours and make them explode. It’s worked in rats, but Erholtz is the first patient to receive such a large dose of measles – literally 100 billion units, enough to vaccinate 10 million people, according to U.S. reports.

There, doctors are working on using viruses to infect and kill cancer cells. It’s a tricky therapy though. For starters, it can only be used once – after that your body’s immune system recognizes the viruses and destroys them before going after the tumours.